Cruising - 1 engine or 2

[sailjumanji]

Seawind 1000 cat, twin 9.9 hp high thrust Yamaha's. With both engines at 3800 rpms, make 5.5 knots and burn 0.8 gal per hour. (They will make 7.2 knots at 5300 rpms, but I choose to not push them like that.) One engine makes 4 knots at same rpms and burns 0.5 gal per hour. Learned all of this motoring across the gulf for five days with zero wind, and not enough fuel to run both engines entire distance. Boat fully loaded coming back from months in Exumas. Have tachs on both motors, and GPS and paddle wheel speed.

[Lizzyfish]

Single engine and a slower speed is most efficient, when doing crossings with cats that is the standard rule!

[valhalla360]

Originally Posted by oleman

This subject has been "studied to death" by the students and staff of the United States Naval Academy in Annapolis. There are many post graduate thesis published on the subject. You can go there for real engineering data that the tax payers of the United States have already paid for.
Basically it is a very complicated engineering subject with NO simple answers.

It's only complicated when asked in the generic theoretical sense.

Otherwise a couple of fuel flow meters and a couple days running at various speeds in various wind/wave conditions...and you can quickly plot up the answers for what is the best option.

[boatman61]

If doing an extended period of motoring.. often in the Med.. I use one engine at around 1500revs with a 5min power burst just before switching to the other engine.. it burns of the crap..
Do this in 4hr periods at change of watch.. keeps engine hours pretty similar..
Two engines are for marina work or heavy headwinds..
Why use double the fuel and shorten engine life for just 1kt gain... poor economy.
Motorsailing I prefer to use the leeward engine as I find it keeps a better heading..

[Factor]

Originally Posted by boatman61

If doing an extended period of motoring.. often in the Med.. I use one engine at around 1500revs with a 5min power burst just before switching to the other engine.. it burns of the crap..
Do this in 4hr periods at change of watch.. keeps engine hours pretty similar..
Two engines are for marina work or heavy headwinds..
Why use double the fuel and shorten engine life for just 1kt gain... poor economy.
Motorsailing I prefer to use the leeward engine as I find it keeps a better heading..

What he said.